The present invention relates to polymer compositions that are water stable on one surface and water-sensitive on the opposing surface. More particularly, the present invention encompasses flushable films that retain their integrity in the presence of body waste fluids, but which disintegrate and disperse in the hydraulic flow of a toilet.
Disposable products have revolutionized modem lifestyle and are of great convenience to society. Such products generally are relatively inexpensive, sanitary and quick and easy to use. Disposal of such products, however, increasingly is a problem as landfills close and incineration contributes to urban smog and pollution. Consequently there is an urgent need for disposable products that can be disposed of without dumping or incineration. An ideal disposal alternative would be the use of municipal sewage treatment and private residential septic systems. Products suited for disposal in sewage systems that can be flushed down a conventional toilet are termed xe2x80x9cflushable.xe2x80x9d An essential feature of flushable products is that they must have sufficient strength for their intended use, yet lose structural integrity upon contact with water.
Numerous attempts have been made to produce flushable fibers, fabrics, films and adhesives that retain their integrity and wet strength in the presence of body waste fluids, yet can be disposed of via flushing in conventional toilets. One approach to producing a flushable product is to limit the size of the product so that it will readily pass through plumbing without causing obstructions or blockages. Such products often have high wet strength and do not disintegrate during flushing. Examples of this type of product include wipes such as baby wipes. This approach to flushability suffers the disadvantage, however, of being restricted to small articles.
Another approach to producing a flushable product is to manufacture a product that is normally insoluble in water, but which disintegrates in the presence of alkaline or acidic aqueous solutions. The end user is provided with an alkaline or acidic material to add to the water in which the product is to be disposed. This approach permits disposal via normal plumbing systems of products substantially larger than wipes, but suffers from the disadvantage of requiring the user to perform the step of adding the dissolving chemical to the water. A further disadvantage is that the inadvertent or intentional disposal of such a product in a conventional toilet without the addition of the dissolving chemical can cause serious obstruction or blockage of the plumbing system. The latter disadvantage can, however, be overcome by incorporating the dissolving acid or alkali into the article but separate from the dissolvable material while in use. The dissolving chemical is only released upon contact with water during flushing.
Similarly, another approach to producing a flushable product, particularly wipes, consists of forming the product from a pH-sensitive gelled polymer, and storing the product in the presence of a separate acidic solution. When the wipe is placed in a large quantity of neutral pH water, it disintegrates as a result of the pH shift. A disadvantage of this pH shift approach to flushability is that some acidic polymers lose wet strength at slightly alkaline pH in the range of 7-8. Because the pH of urine may be as high as 8.5, these flushable materials are not well suited for use in, for example, diapers or incontinence pads.
Another approach to producing a flushable product is to form the product from material that is susceptible to attack by specific enzyme catalysis that breaks down the structural integrity of the material. In such a product the enzymes may be introduced into the disposal water separately. These systems suffer many of the same disadvantages as those described above for alkaline or acid treatable materials.
UK patent application GB 2 083 762A to Enak Limited discloses an ostomy pouch where a water impermeable layer of polyvinylidene chloride, vinyl chloride-vinylidene chloride-copolymer, atactic polypropylene, nitrocellulose, waxes, greases, silicone, or pressure sensitive adhesives is backed by a layer of polyethylene oxide or polyvinyl alcohol. However, this construction may not be mechanically weak enough in the flow of toilet water to disintegrate sufficiently.
UK patent application GB 2 185 404A to Smiths Industries Public Limited Co. discloses an ostomy bag with an inner layer of polyvinylidene chloride is backed by a layer of polyvinyl alcohol. However, this construction may not be mechanically weak enough in the flow of toilet water to disintegrate sufficiently.
U.S. Pat. No. 4,732,311 to J. E. Potts discloses coating a water soluble polymer, such as polyethylene oxide with a degradable water-insoluble polymer such as a cyclic ester polymer, a poly(beta-hydroxy butyrate), dialkanoyl polymers, such as polyesters and polyurethanes derived from aliphatic polyols, and ethylene polymers.
U.S. Pat. No. 5,283,090 to Y. Umemura discloses a multi-layered urine or ostomy bag, the inner side of which is water-impermeable by means of silicon or fluorine-containing coatings such as polytetrafluoroethylene and methylhydroxypolysiloxane. The sheet may be made of polyvinylpyrrolidine, polyacrylamide, polyvinyl ethers, polyethylene oxide, methyl cellulose, ethyl cellulose, carboxymethyl cellulose, hydroxyethyl cellulose, polyvinyl alcohol, polyacrylic acid and polymethacrylic acid, and isobutene-maleic acid copolymers.
U.S. Pat. No. 5,110,390 to F. Martini, et al., discloses an ostomy bag of a laminate of a water-disintegratable film such as polyvinyl alcohol or polyethylene oxide, and a coextruded film of vinylidene chloride polymer or ethylene copolymer which includes a melt-bondable layer.
U.S. Pat. No. 5,300,358 to G. R. Evers discloses a flushable structure for absorption of body fluids composed of an absorbent degradable fibrous core and a backsheet that is cold-water soluble, but water impermeable.
U.S. Pat. No. 5,468,526 to S. I. Allen, et al., discloses an ostomy bag composed of a homopolymer of vinylidene chloride or methylmethacrylate coated onto a water soluble film layer of a blend of polyvinyl alcohol, polycaprolactone, or polyethyloxazoline and a thermoplastic polyurethane.
U.S. Pat. No. 5,578,344 to N. A. Ahr, et al., discloses a process for impregnating a resin onto a substrate to form a web, where the exposed side of the web is dispersible in water, while the impregnated side is water resistant.
None of the above methods and articles have proven entirely satisfactory. Therefore, there is a need for a flushable product which is not limited in size and which does not require special conditions of disposal.
The present invention provides a composition comprising a low-molecular weight, amorphous polyalphaolefin layer and a water-sensitive substrate layer. Preferably, the polyalphaolefin is a poly(propylene-ethylene) copolymer or a poly(ethylene-butene) copolymer. When the composition is employed as a diaper outer cover or a pantiliner baffle, for example, the polyalphaolefin layer is exposed to bodily fluids, and inhibits their transport to the water-sensitive layer. When the entire article is disposed of in a toilet, however, the water-sensitive layer is wetted and weakens. Since the low-molecular weight amorphous polyalphaolefin layer is already mechanically weak without the support of the water-sensitive layer, the hydraulic force of the toilet flow causes the composition to disperse into pieces small enough to flow through the toilet and beyond without clogging the water system.
It is, therefore, desirable to provide disposable products that can be flushed in a conventional toilet with subsequent product dispersion into pieces that can be managed by standard sewage treatment or home septic systems. Additionally, it is desired to provide disposable products that can be flushed in a conventional toilet without the addition of a dissolving chemical. Finally, it is desired to provide flushable products that are insoluble in the presence of body waste fluids, but which are water soluble in the presence of normal toilet water.
Polyalphaolefins are widely used as adhesives. However, their value as a barrier layer for a water-sensitive substrate has not been previously recognized. The inventors have discovered that these polyalphaolefins provide an effective barrier layer against fluids, thereby permitting films having a layer of a polyalphaolefin to be used in a variety of different applications, such as disposable personal care products.
The present invention provides a two-layer film composition, comprising a low molecular weight amorphous polyalphaolefin layer joined to a water-dispersible substrate layer. In general, a melt viscosity in excess of 10,000 cps at 190xc2x0 C. is indicative of higher molecular weight polyalphaolefins, while a melt viscosity of less than 10,000 cps at 190xc2x0 C. is indicative of low molecular weight polyalphaolefins. Desirably, amorphous polyalphaolefins useful in the present invention are low molecular weight polyalphaolefins having a melt viscosity of about 400 to about 10,000 cps at 190xc2x0 C. Preferably, the polyalphaolefin comprises propylene-ethylene copolymers or ethylene-butene copolymers. The compositions of the present invention have sufficient strength for their intended use, yet are dispersible into pieces under the hydraulic force of normal tap flow or toilet water flow.
Films of the present invention can be widely used as components of such disposable goods as sanitary napkins, pantiliners, diapers, bandages, and the like. Such films, if they are to function effectively, must maintain their structural integrity, as well as exhibit satisfactory tensile strength, when they are wet or damp with various body fluids. These body fluids include blood, menstrual fluid, vaginal exudate, urine and perspiration, which the films will contact during use. It has been recognized that if such films, while retaining their strength in body fluids, were to lose their integrity when exposed to water and become readily dispersible therein, disposal problems would be substantially eliminated, since the films could be easily and conveniently disposed of by contacting the film with water. The present invention provides a mechanism for eliminating disposal problems associated with various consumer products.
The present invention can be described as a flushable film composition comprising a layer of a hydrophobic, low molecular weight, amorphous polyalphaolefin resin joined to a water-dispersible substrate. The polyalphaolefin layer preferably comprises propylene-ethylene copolymers or ethylene-butene copolymers. The compositions of the present invention can further comprise an absorbent layer of material adjacent the hydrophobic, polyalphaolefin layer opposite the side joined to the water-dispersible substrate layer. The absorbent layer can comprise synthetic and natural materials well-known in the field of diapers and pantiliners for example, which are generally very fibrous, porous and hydrophilic.
In a further embodiment of the present invention, the film composition may serve as a primer layer for additional coatings on the water-dispersible substrate, such as latex coatings. The primer layer provides enough water protection so that a water-based solution coating may be applied to the coated water-dispersible film, the water being subsequently removed prior to any degradation of the water-dispersible substrate layer. In most cases and applications, the coated water-dispersible film is flushable because it will disperse rapidly when exposed to the hydraulic water flow in a conventional toilet.
The term xe2x80x9cflushablexe2x80x9d as used herein means capable of being flushed in a conventional toilet, and being introduced into a municipal sewage or residential septic system, without causing an obstruction or blockage in the toilet or sewage system.
The term xe2x80x9camorphousxe2x80x9d as used herein means a polymer having a degree of crystallinity of less than about 20%. Since the polyalphaolefin layer of the present invention is amorphous and of a low-molecular weight, it is weak, and the thin coating breaks apart very easily when the water-dispersible substrate begins to disperse. The amorphous character of the polyalphaolefin layer precludes any substantial crystal formation, and any associated crystalline brittleness in the coating. The amorphous character also provides adhesive tack for the coating to adhere well to the water-dispersible substrate.
The polyalphaolefin coated water-dispersible films of the present invention may be used in the preparation of a wide variety of products designed to be contacted with aqueous fluids. Although the coated water-dispersible film of the present invention is particularly suited for personal care products, the coated water-dispersible film of the present invention may be advantageously employed in the preparation of a wide variety of consumer products other than personal care products.
For a flushable composition of the present invention, such as a diaper outer cover or a pantiliner baffle, the inner side of the compositionxe2x80x94the side closer to the wearer of the articlexe2x80x94will typically be exposed to body fluids in use, while both sides will be exposed to toilet water in disposal. The polyalphaolefin coating on the side adjacent to the wearer of the article inhibits the transport of body fluids through the composition, and provides a barrier between body fluids and the water-dispersible substrate on the outer surface. However, the side of the article further from the wearer of the water-dispersible substrate is designed to quickly weaken in the flow of toilet water, and allows the entire composition to lose enough structural integrity to flush down a conventional toilet. Preferably, the substrate has a peak-load strength of less than 20 g/in, which is comparable to wet bathroom tissue.
A coating of a low molecular weight amorphous polyalphaolefin polymer provides a substantial barrier to body fluids, yet has very little mechanical strength. It therefore loses its mechanical integrity when the water-dispersible substrate disperses in the hydraulic flow of plain toilet water. Desirably, the low molecular weight amorphous polyalphaolefin has a melt viscosity of about 400 to about 10,000 cps at 190xc2x0 C. As a polyalphaolefin, the coating is hydrophobic, and so provides a good water barrier even in thin layers. The invention provides that the amorphous polyalphaolefin layer can be between about 0.1 to 5 mils thick, and preferably about 0.5 to 2.0 mils thick. The low molecular weight and relative thinness ensure that the coating has little mechanical integrity of its own; little force is required to pull the coating into pieces, as measured in a test of wet tensile strength.
Amorphous polyalphaolefin polymers that can be used in the present invention include, but are not limited to, propylene-ethylene copolymers and ethylene-butene copolymers. Desirable polyalphaolefin polymers include REXTAC(copyright) polymers, which are available from the Rexene Corporation (Dallas, Tex. 75244) under the designation RT2315, RT2535. In general, the REXTAC(copyright) polymers are low density (0.86 to 0.88 g/cc), low molecular weight polyalphaolefins. Each of the REXTAC(copyright) polymers has a melt viscosity of from about 400 to about 10,000 cps at 190xc2x0 C. and a tensile strength of from about 0.25 to about 1.5 MPa.
Suitable polymers for the water-dispersible substrate layer include, but are not limited to, polyalkylene oxides, such as polyethylene oxide (PEO), ethylene oxide-propylene oxide copolymers, polymethacrylic acid, polymethacrylic acid copolymers, polyvinyl alcohol, polyethyl oxazoline, polyvinyl methyl ether, polyvinyl pyrrolidone/vinyl acetate copolymers, methyl cellulose, ethyl cellulose, hydroxypropyl cellulose, hydroxypropyl methyl cellulose, ethyl hydroxyethyl cellulose, methyl ether starch, poly (n-isopropyl acrylamide), poly N-vinyl caprolactam, polyvinyl methyl oxazolidone, polyvinyl methyl oxazolidimone, poly(2-isopropyl-2-oxazoline), and poly (2,4-dimethyl-6-triazinyl ethylene).
The water-dispersible substrates of the present invention may be made entirely of water-dispersible polymeric material or may contain water-dispersible as well as water-insoluble materials so long as the film disperses in water, such as in the hydraulic flow of a conventional toilet. Additionally, water-dispersible films may also be made by mixing various different types of water-dispersible film materials. In some embodiments, it may be desirable to employ one or more additives into the water-dispersible film material including, but not limited to, compatibilizers, processing aids, plasticizers, tackifiers, detackifiers, slip agents, and anti-microbial agents, as fabricating agents or as modifiers depending on the specific properties desired in the film and the final product.
Additionally, in another embodiment, the amorphous, low molecular weight polyalphaolefin may be admixed with a paraffin wax, such as a highly branched hydrocarbon. These hydrocarbons help to lower the wet strength of the film while maintaining barrier strength. One such paraffin wax is VYBAR(copyright) 253 polymer from Petrolite Corp. (Tulsa, Okla.). Preferably, the wax is admixed in an amount from about 1 to about 20 percent by weight. More preferably, the wax is admixed in an amount of about 10 percent by weight.
Desirably the water-dispersible film of the present invention comprises a polyalkylene oxide film or a polyvinyl alcohol film. More desirably, the water-dispersible film of the present invention comprises a polyethylene oxide film, an ethylene oxide-propylene oxide copolymer film, a polyvinyl alcohol film or a film derived from a polyvinyl alcohol copolymer. Most desirably, the water-dispersible film of the present invention comprises a polyethylene oxide film or a polyvinyl alcohol film. The polyethylene oxide film is the most desirable film for a transfer coating procedure, while the polyvinyl alcohol film is the most desirable film for a direct coating procedure. The thickness of the water-dispersible film may vary greatly depending upon the end use of the film-containing product. Film thickness should be minimized when possible to reduce product cost and to reduce the time necessary for the film to disperse, especially in the case of flushable products. Desirably, the water-dispersible substrate will be between about 0.1 to 10 mils thick, or more desirably about 1 to 2 mils thick.
The polyalphaolefin layer may be joined to the water-dispersible substrate by standard methods known to those of ordinary skill in the art. As mentioned, the polyalphaolefin layer itself can provide enough tack to join the water-sensitive substrate layer thereto. Other suitable methods of joining the layers include, but are not limited to, solvent-based coating and hot-melt coating. Suitable solvent-based coating techniques include, but are not limited to, spray coating and ink jet printing. Suitable hot-melt coating techniques include, but are not limited to, slot coating, screen coating, spray coating, swirl coating and gravure coating. Another suitable method includes a transfer coating procedure.
The preferred coating process is a hot-melt slot die process. Molten polyalphaolefin polymer is delivered from a melting tank through a heated hose to a slot die. The temperature of the melting tank, hose and slot die may vary depending upon the melt rheology of the polyalphaolefin in the coating process. The molten polymer is uniformly applied directly onto the water-sensitive film, or alternatively, onto a carrier substrate and subsequently transferred onto the water-sensitive film (transfer coating process). Line speeds may vary depending upon the xe2x80x9copen timexe2x80x9d of the polyalphaolefin. As used herein, the xe2x80x9copen timexe2x80x9d of a polymer refers to the amount of time required for the polymer to lose its tackiness.
In a transfer coating process, the coated carrier substrate moves further through the process and comes into contact with the water-sensitive film, which is properly aligned with the coated carrier substrate. The coating is transferred from the carrier substrate to the water-sensitive film under pressure as the film and carrier substrate pass through a nip roll. In practice, optimum coating thickness is achieved by adjusting processing factors which include, but are not limited to, the polyalphaolefin, the coating temperature, the resin flow rate, line speed, and the pressure applied at the nip roll.
In the transfer coating process or in a contact direct coating process, such as screen printing, the adhesion of the polyalphaolefin coating to the water-sensitive film should be greater than the adhesion of the polyalphaolefin coating to the screen (direct coating) or the carrier substrate (transfer coating). The choice of polyalphaolefin should take into consideration the desired characteristics and properties of the polyalphaolefin. The polyalphaolefin should have good adhesion to the water-sensitive substrate.
Those skilled in the art will readily understand that the polyalphaolefin coated water-dispersible films of the present invention may be advantageously employed in the preparation of a wide variety of products designed to be contacted with aqueous fluids. Although the coated water-dispersible film of the present invention is particularly suited for personal care products, the coated water-dispersible film of the present invention may be advantageously employed in the preparation of a wide variety of consumer products other than personal care products.
The present invention is further illustrated by the following examples, which are not to be construed in any way as imposing limitations upon the scope thereof. On the contrary, it is to be clearly understood that resort may be had to various other embodiments, modifications, and equivalents thereof which, after reading the description herein, may suggest themselves to those skilled in the art without departing from the spirit of the present invention and the scope of the appended claims.